1. Field of the Disclosure
This disclosure relates to a light irradiation apparatus adapted to photo-process an alignment film of a liquid crystal display panel.
2. Description of the Related Art
Display device markets have changed in the center of flat panel display devices, which have a light weight and are thin, unlike the previous CRT (cathode ray tube). The flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panels (PDPs), light emitting diode (LED) display devices, and others.
Among the flat panel display devices, LCD devices each can include an LCD panel, a driving unit, and a backlight unit. The LCD panel displays an image on it. The driving unit applies driving signals to the LCD panel. The backlight unit applies light to the LCD panel.
The LCD panel includes first and second substrates disposed opposite each other and combined to maintain a cell gap between them, and a liquid crystal layer interposed between the substrates.
On the first substrate, a plurality of gate lines are formed, a plurality of data lines are formed to cross the plurality of gate lines, and a plurality of transistors TFT are formed at the intersections of the plurality of gate lines and the plurality of data lines. The first substrate is divided into a plurality of pixel regions by the crossing of the gate and data lines.
The second substrate includes a black matrix and a plurality of color filters. The black matrix is used for blocking light on the regions that are not the pixel regions. The plurality of color filters are used for realizing colors.
Also, alignment films are formed on the first and second substrates, respectively. To form the alignment films, a rubbing process is mainly used. The rubbing process forms an alignment film by coating an alignment material such as PI (polyimide) on a substrate and putting a rubbing cloth into physical contact with the substrate on which the alignment film is formed. The physical contact allows an alignment film to have an alignment direction. Such a rubbing process makes it possible to process at high-speed an enlarged sized of alignment film. Therefore, the rubbing process is widely used in the formation of an alignment film.
However, the rubbing process causes fine flaws on the alignment film due to unevenness in rubbing strength, so that liquid crystal molecules are not uniformly oriented. As such, irregular phase distortion and light dispersion are caused. Accordingly, the performance of the LCD device is deteriorated. Moreover, since the rubbing process may generate static electricity and contamination of the alignment film by fine dust and particles, the productive ratio of LCD device (and/or panel) is reduced.
To solve the problem in the rubbing process, a variety of photo alignment methods have been researched. Among the photo alignment methods, a UV alignment method has been highlighted which irradiates UV (ultraviolet) light on a high polymer film in order to form a liquid crystal alignment film.
The photo alignment method using UV light eliminates the possibility of causing static electricity and the contamination of the alignment film and prevents the decrement of the productive ratio of the LCD device (and/or panel). Also, the UV alignment method allows liquid crystal molecules to be uniformly oriented on the entire surface of the alignment film, thereby enhancing the alignment degree of liquid crystal molecules.
However, the photo alignment causes undesired reactions, such as a photo-oxidation reaction and others, due to the shorter wavelength light being below an effective wavelength for the photo alignment on the high polymer film. The undesired rejection reaction generates carboxylic acids which are included in a functional material group. As the carboxylic acids largely affect a residual image on the LCD device, the UV alignment method has recently revealed a serious problem of generating these carboxylic acids.